1. Field of the Invention
The present invention relates to a hydraulic system for a double piston. More particularly, the present invention relates to a hydraulic system for a double piston without a solenoid valve for controlling a switch valve.
2. Description of Related Art
Recently, the one-way clutch connected with a low & reverse clutch used at a first forward speed range of a transmission is being gradually removed for enhancement of fuel consumption, reduction of weight, and reduction of cost.
In using a one-way clutch of the related art, there is little shift shock because mechanical shifting is possible by the one-way clutch without a specific limit in a low & reverse clutch in shifting with a large torque change such as 1→2 or 2→1, while it is required to precisely control the low & reverse clutch by removing the one-way clutch.
In general, the low & reverse clutch is used at the first forward speed range and a reverse speed range, and when there is a change in allotted torques of the first forward speed range and the reverse speed range, the allotted torques is set to the larger speed. In this case, it is more difficult to control precisely with a relatively small torque.
For example, when the allotted torque of the reverse speed range is larger in the allotted torques of the first forward speed range and the reverse speed range, the clutch allotted torques are set on the basis of the reverse speed range, such that an allotted torque larger than the necessary allotted torque is set for the first forward speed range.
Therefore, in general, when two shifting speeds are set by one clutch, a double piston structure is used, a switch valve is used to control the double piston valve, and a switch valve solenoid valve is necessary to operate the switch valve.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.